#define _CRT_SECURE_NO_WARNINGS 1

#include<stdio.h>

int main()
{
	float sum = 0;
	for (int i = 1; i <= 100; i++) {
		int x = i % 2;
		if (x == 0) {
			sum += -1.0 / i;
		}
		else {
			sum += 1.0 / i;
		}
	}
	printf("%f", sum);
	return 0;
}